As wireless telecommunication systems become more and more common, the aim is to increase the performance of radio systems as close to a theoretical maximum as possible. In this development work, the dynamics of the transmission power of transmitters plays an important role. The required transmission power of a transmitter may change due to external reasons, such as a change in the radio transmission path between the radio transmitter and a receiver or when the radio transmitter starts or stops transmitting an active time slot.
Good transmission power dynamics of radio systems requires that the output power of power amplifiers of transmitters should be provided with a wide operating range. It is typical for the power amplifiers used in radio systems that high output power of a power amplifier provides good efficiency but, at the same time, the linearity of the power amplifier is reduced. A power amplifier operating at a good efficiency level thus causes non-linear distortion to an amplified signal or, alternatively, a power amplifier operating within a linear range operates at a poor efficiency level, wasting power.
In the prior art solutions, a transmitter may operate at two or more power levels that are determined according to the transmission power needed. The power levels are provided by changing the power of a signal supplied to the power amplifier, and simultaneously optimizing the operating point of the power amplifier in order to minimize power consumption. A drawback of the prior art solutions is the slow response of the element used for controlling the operating voltage of a power amplifier and the resulting delay in achieving the desired amplification of the power amplifier in proportion to the necessary rate of change in the transmission power. The delayed amplification of the power amplifier causes distortions in the amplified signal, impairing the performance of a radio system.